The present disclosure relates to a catalyst device provided in the exhaust system of an internal combustion engine.
A type of catalyst device that includes a catalyst support, a tubular portion, and a holding mat has been known. The catalyst support supports a catalyst that purifies exhaust gas of the internal combustion engine. The tubular portion accommodates the catalyst support. The holding mat is arranged between the catalyst support and the tubular portion to hold the catalyst support in the tubular portion. For example, refer to Japanese Laid-Open Patent Publication No. 2004-176553.
By providing an insulator over the outer circumferential surface of the tubular portion and a heat insulating member between the tubular portion and the insulator, the tubular portion is covered with the heat insulating member. Since this configuration reduces the heat radiation amount of the tubular portion, the temperature increase of the catalyst support due to the exhaust heat is further promoted. This improves the exhaust purification performance.
If the tubular portion is covered with a heat insulating member, the diameter expansion amount of the tubular portion due to thermal expansion increases in the entire tubular portion, increasing the clearance between the tubular portion and the catalyst support. This reduces the holding force of the holding mat, which is arranged in the clearance in a compressed state. When the holding force of the holding mat decreases, the catalyst support, of which the outer circumferential surface is wrapped with the holding mat, may move downstream in the exhaust gas flowing direction, for example, due to factors such as the exhaust pressure. In this case, there is a possibility that the arrangement position of the catalyst support may be displaced in the tubular portion.